package/rpm: fix build with NLS

Add TARGET_NLS_LIBS to LIBS to definitely fix linking with lintl instead
of calling autoreconf

Fixes:
 - http://autobuild.buildroot.org/results/a1446b419f5f59f65fe80849182e38457de203b5



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>